Clastic and carbonate rocks are produced from "exogenous,muddy water" and "endogenous,clean water" environment,respectively.The frequent alternations of clastic and carbonate facies reflect the repeated,major changes in multiple environmental factors,such as the nature of palaeowater,sediment supply and palaeoclimate.During the Late Carboniferous,the northern Qaidam Basin is tectonically inactive,and thus providing conditions for development of extremely thick mixed clastic-carbonate deposits,which consist of multistage cycles,recording "icehouse" information such as the glacier activities and their influence to the palaeo-sea level fluctuations as well as the frequent palaeoclimate and palaeoenvironment changes.The continuous outcrop and core section from the northern Qaidam Basin are taken as the research object.In association with regional geological data and previous research results,we identify the clastic incised-valley fills and carbonate platform deposits,which are frequently alternated and constituted the mixed strata,in the target interval of the study area.The orderly superposition of the clastic-carbonate sequence succession in the vertical direction constitutes a complex sea-level change cycle sequence.The vertical change from the deformed carbonate platform to the lower river-dominated incised valley and then to the upper estuary bay-fill sequence towards flooding mudstone,into the carbonate platform from seaward to landword,suggesting a complex sea-level change cycles,which are expressed as the early regression initially—the gradual transgression in the middle period—the returned regression in the later stage.The obviously cold climate weather during the glacier period and the intensive glacioeustatic change,with high-amplitude sealevel rise and fall,have driven the migration of the shorelines and facies belts,and have contributed to the clastic-carbonate successions by affecting the supply rate of the clastic rocks and the productivity of the carbonate rocks,leading to the frequent conversion of clastic and carbonate strata.%碎屑岩和碳酸盐岩分别产自“外源、浑水”与“内源、清水”环境,二者的交替互层沉积可反映古水体性质、物源供给及气候等环境要素的频繁改变.晚石炭世,柴达木盆地北缘构造相对稳定,盆内发育巨厚的、多级次嵌套的“碎屑岩—碳酸盐岩混积层系”,记录了“冰室地球”冰川活动下的古海平面大幅度升降和古气候、古环境频繁交替信息.文中以柴达木盆地北缘连续完整露头剖面和钻井取心剖面为研究对象,结合区域地质资料、前人研究成果,通过详细的岩心、露头及镜下薄片观察,在研究区重点层段识别出下切谷充填型碎屑岩沉积和碳酸盐岩台地沉积组成的频繁互层序列.碎屑岩—碳酸盐岩互层组合序列在垂向上的有序叠加,构成了复合海平面变化旋回层序,其从碳酸盐岩—改造型台地沉积开始,向上依次发育碎屑岩下切谷充填序列的底部冲积河道沉积、中部河口湾序列和顶部代表海泛面的泥岩沉积,最后转变为碳酸盐岩向海到向陆台地亚相,反映了一个显著的早期海退—中期逐渐海侵—后期再次海退的旋回过程.冰川期急剧变冷的气候和冰川型高频的大幅度海平面升降,驱动滨线及相带迁移,影响到碎屑岩供给速率和碳酸盐生产率,造成了碎屑岩—碳酸盐岩的高频转换.
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